The present invention relates to a brake wear detection device for trailer units (2), comprising an electrical circuit (4), normally closed, that is fed from the tractor unit (1). It connects the entire series of conventional devices for detecting wear and tear in the lining of brake shoes or pads located in each of the wheels (2a-2f) of the trailer unit, and which is connected to a relay (3) that is able to induce the closure of an additional circuit (5), which is normally open, that is also connected to the same relay.

It is advantageous to equip any trailer unit hooked up to a tractor unit, such as trailers for buses, trucks, tractors, cars, caravans, and so on, with braking devices independent of the braking devices of the tractor unit, in order to limit the inertial effect of the trailer against the aforementioned tractor when the tractor unit brakes. When operated together from the tractor, both braking systems can act independently or in synch.